1. Field of the Invention
The invention relates to a vehicle behavior control system, and particularly, a vehicle behavior control system that obtains a value that indicates a normal vehicle state (hereinafter referred to a normal vehicle state value) based on an operating amount of a vehicle operator with respect to a vehicle operating member so as to control the vehicle behavior based on an actual vehicle state value and the normal vehicle state value.
2. Description of Related Art
Conventionally the aforementioned behavior control system for vehicle, for example, an automobile is disclosed in Related Art No. 1 (JP-A-8-310366). In the publication, the normal vehicle state value is obtained based on an amount of steering performed by a vehicle operator, the behavior of the vehicle is estimated based on the normal vehicle state value and the actual vehicle state value. The target vehicle state value is further obtained based on the estimated vehicle behavior. Finally the vehicle behavior is controlled by controlling the braking device based on the obtained target vehicle state value.
In the aforementioned vehicle behavior control system, if the vehicle behavior is deteriorated, that is, it is brought into the condition of spin or drift out state, a target vehicle state value to stabilize the vehicle behavior is calculated based on such deteriorated behavior so as to regulate the braking device in accordance with the target vehicle state value. This makes it possible to stabilize the vehicle behavior by establishing the target vehicle state value.
Related Art No. 2 (JP-A-11-173176) discloses the vehicle attitude control system that adjusts an engine output in accordance with a degree of counter steering operation. Related Art No. 3 (JP-A-10-315941) discloses the vehicle behavior control system that appropriately controls the turning behavior of the vehicle in accordance with a steering operation of the vehicle operator by reducing the control response upon the counter steering.
In the case where the braking force is applied to the vehicle that is running on the road having a friction coefficient that varies depending on the right side of the road corresponding to the right wheels of the vehicle and the left side of the road corresponding to the left wheels of the vehicle, i.e., the road with uneven friction coefficient, the vehicle tends to be directed to the road side having higher friction coefficient owing to the difference in the applied braking force between the right wheels and the left wheels. Accordingly the vehicle operator tries to perform steering toward the direction such that the aforementioned deflection of the vehicle is corrected. The vehicle behavior control system as described above will reduce the braking force applied to the wheels corresponding to the road side with the higher friction coefficient to decrease the yaw moment resulting from the difference in the braking force between the right wheels and the left wheels for stabilizing the behavior of the vehicle in the aforementioned condition. The aforementioned efforts to stabilize the vehicle behavior and to secure the reliable braking force applied to the vehicle, thus, contradict with each other. It is preferable to execute the vehicle behavior control that requires an effort of the vehicle operator to correct the steering operation so as to stabilize the vehicle behavior during braking operation of the vehicle running on the road with uneven friction coefficient.
In the aforementioned vehicle behavior control system as disclosed in the above-identified publications, the normal vehicle state value is obtained based on the amount of steering performed by the vehicle operator without considering the correction of the steering performed by the vehicle operator. Then the vehicle behavior is estimated based on the obtained normal vehicle state value and the actual vehicle state value. The target vehicle state value is then obtained based on the estimated vehicle behavior. The aforementioned system, therefore, fails to execute the appropriate vehicle behavior control in consideration with the correcting steering operation performed by the vehicle operator.